/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformString.h
Returns the required buffer length for the null-terminated Src string when converted to the DestChar encoding. The returned length includes the space for the null terminator (equivalent to strlen+1).
The number of DestChar elements that Src will be converted into.
template<typename DestEncoding, typename SourceEncoding> static int32 ConvertedLength ( const SourceEncoding * Src )